1. Field of Invention
The present invention relates generally to a chemical mechanical planarization system. More specifically, the invention relates to a method and apparatus for conditioning polishing pads of a chemical mechanical planarization system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to deposit multiple layers on a substrate for electronic devices. As the demand for planarization of wafers in semiconductor fabrication increases, the requirement for greater system (i.e., tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two such CMP systems that address these issues are described in a patent to Perlov et al. (U.S. Pat. No. 5,804,507, issued Sep. 8, 1998) and in a patent to Tolles et al. (U.S. Pat. No. 5,738,574, issued Apr. 15, 1998), both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization apparatus that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. From the transfer station, the wafers are loaded to a processing head. A carousel delivers the processing head and wafer to various planarization stations where the wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry. The polishing pad may include an abrasive surface. Additionally, the slurry may contain both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Another system is disclosed in a patent to Hoshizaki et al. (U.S. Pat. No. 5,908,530, issued Jun. 1, 1999) which is hereby incorporated by reference. Hoshizaki et al. teaches an apparatus for planarizing wafers wherein the wafer is subjected to uniform velocity across the wafer surface with respect to the abrasive surface. The uniform velocity across the wafer surface coupled with a multi-programable planarization pattern results in a uniform rate of material removal from the wafer surface. In addition, Hoshizaki et al. provides a number of optional routines that allow a user to fine tune material removal from the wafer.
The systems described above can generally utilize polishing pads with and without abrasive finishes. The polishing pads may be stationary or move relative to the wafer. Additionally, abrasive slurry, de-ionized water and other fluids may be disposed on the polishing pad during the processing of the wafer.
Common to these and other planarization systems, is the need to periodically condition the pad or polishing media. During the planarization process, the polishing media may become worn from contact with the wafer and polishing slurry. Fixed abrasives often used in polishing media may also have the abrasive particles dislodged during processing. Additionally, material removed from the wafer may become impacted or clog the surface topography of the polishing media. Worn, damaged and clogged polishing pads may cause inconsistent material removal from the wafer that can result in less than desirable planarization and may cause other surface defects (i.e., scratching) that may render the wafer defective.
An approach typically used to condition the polishing media (i.e., creating or returning the polishing media to an optimized state for wafer processing) is to dress the polishing media. Dressing typically includes moving a biased brush, or a single patterned plate against the polishing media, spraying fluids against the polishing media, applying mega or ultra sonic energy to the polishing media or xe2x80x9cvacuumingxe2x80x9d the surface of the polishing media. Often, this process occurs at the working region by scanning the dressing device across the polishing pad in a pattern similar to the planarization pattern. These dressing processes (interchangeably referred to as conditioning processes) are periodically employed to return the polishing media to a state that produces acceptable planarization without damaging the wafer. Generally, either a conditioning device is set in the polishing head or the polishing media is conditioned periodically between wafer processing runs. Disadvantageously, both of these methods result in diminished wafer throughput since the processing of wafers is halted while a working region of the polishing media is conditioned.
A device that provides an improvement over the typical conditioning process is a xe2x80x9cPolishing Media Magazinexe2x80x9d coupled to a planarization system disclosed in the commonly assigned U.S. patent application to Sommer (U.S. patent application Ser. NO. 08/961,602, filed Oct. 31, 1997 and hereinafter referred as xe2x80x9cSommer ""602xe2x80x9d). The Sommer ""602 patent application is hereby incorporated by reference.
Sommer ""602 discloses a polishing media in the form of a web. The web passes from a supply roll through the working region of the processing system to a take-up roll. A conditioning system is disposed between the supply and take-up roll. The conditioning system is positioned outside a working region so that the entire width of the polishing media can be conditioned as the web advances. Conditioning the entire width of the polishing media in one pass results in better utilization of tool time and a corresponding increase in wafer throughput as compared to traditional pad conditioning processes such as scanning the work surface with the dressing device. However, faster conditioning and more versatile conditioning of the polishing media is desirable to increase wafer throughput, minimize wafer damage and enhance wafer planarization.
Therefore, there is a need for a method and apparatus for conditioning polishing pads.
One aspect of the present invention generally provides an apparatus for conditioning a polishing surface. In one embodiment, the apparatus comprising polishing head having a ring disposed on a perimeter of the ring, the ring having a conditioning surface is provided. Another embodiment of the invention provides polishing media, a first conditioning and a second conditioning device that are actuated to contact the polishing media with opposing rotational velocities.
In another embodiment of the invention, a free standing conditioning system for conditioning the surface of a web is provided. In one embodiment, a conditioning system includes an unwind, a conditioning module and a winder. The conditioning module comprises one or more of the conditioning devices selected from the group of devices including at least a first and a second conditioning plate selectively contacting a working surface of the polishing media while rotating in opposite directions, one or more brushes, one or more water jets, one or more wave energy devices and one or more vacuum devices.
In another embodiment of the invention, a polishing table, a web of polishing media having at least a portion disposed on the polishing table, and a conditioning device selectively disposed to contact the polishing media is provided. Additional embodiments of the conditioning device further include retaining rings, rods, disks and cylinders. Optionally, the conditioning devices may be moved or rotated.
In another aspect of the invention, a method for processing a substrate in a polishing system is provided. In one embodiment, a method includes processing a substrate on a portion of media; and conditioning another portion of the media. In another embodiment, a method includes advancing a web of polishing material and conditioning the polishing material.